Terminal Series – Article 7
Terminal Series – Article 7 Contributed by Trey Hess P.E., Principal, PPM Consultants
Every terminal has one: that stubborn corner of the yard where old impacts linger, monitoring wells outnumber forklifts, and “We’ve been watching that plume for years” becomes part of the site tour. It’s not that nothing is happening underground—it’s that the cleanup isn’t aligned with how the terminal actually works above ground. Monitored Natural Attenuation (MNA), paired with sharp institutional controls (ICs), offers a different approach: let nature carry the load, and let operations define the guardrails.
Done right, MNA is not passive—it’s precision. It uses biology, hydrogeology, and smart controls to reduce real exposure risk while keeping the terminal humming. At many bulk liquid terminals, MNA paired with ICs becomes the rare remedy that protects people, accelerates closure, and minimizes disruption.
This article lays out a terminals-first strategy: when MNA is appropriate, how to prove it works, how states handle ICs, and how to build a durable program that fits seamlessly into SPCC, FRP, stormwater, and MOC systems.
What MNA Means at a Working Terminal
MNA relies on natural processes, mostly biodegradation, to reduce dissolved petroleum constituents. Microbes do the heavy lifting, consuming BTEX and pairing them with oxygen, nitrate, or sulfate to create benign end-products.
The science is reliable. The challenge is the terminal environment—drainage edits, utility repairs, containment upgrades, contractor work, and seasonal shifts can all disrupt natural cleanup conditions. That’s why MNA succeeds only when paired with institutional controls that keep exposures closed and subsurface conditions stable.
When MNA Fits (and When It Doesn’t)
Good candidates:
- Dissolved BTEX plumes with stable or contracting footprints
- No free product or a thin smear zone that is not re-mobilizing
- Receptor exposure is controlled or eliminated by policy or engineering
- Supportive geochemistry showing active attenuation
Poor candidates (or those needing pre-treatment):
- Persistent free product or an actively feeding source
- Uncontrolled receptors or confirmed vapor intrusion
- Highly heterogeneous geology that obscures plume trends
If one element is missing, light-touch source work (oxygen release, minor product recovery, or isolation) can prime the site for MNA.
Build a Terminal-Ready Conceptual Site Model (CSM)
A clean, visual CSM is the anchor for the entire program. It should show:
- Sources & pathways: racks, manifolds, utility bedding, outfalls
- Hydrogeology: groundwater depth, gradients, seasonal changes
- Receptors: workers, buildings, stormwater discharge points, groundwater users
- Controls: coatings, joint sealing, drain isolation, dewatering SOPs, ventilation, and proposed ICs
This front-page CSM survives turnover and helps operations understand the “why” behind each control.
Lines of Evidence: Demonstrating Attenuation
A defensible MNA program uses five simple lines of evidence:
- Plume behavior: stable or shrinking boundaries
- Geochemistry: DO/ORP trends and electron acceptor usage
- Mass balance/rates: first-order decay or electron acceptor balances
- Vapor checks: as needed, with clear triggers
- Hydraulic stability: gradients consistent with the plume shape
One chart per line of evidence—kept consistent quarter to quarter—is usually what regulators need.
Institutional Controls: The Guardrails That Make MNA Work
MNA only works when the rules that keep exposure pathways closed are clear, visible, and enforceable. These rules live in ICs.
How Mississippi, Alabama, Florida, Georgia, and Louisiana Establish ICs
Mississippi – Environmental Covenants (UECA)
- Recorded covenant running with the land
- Activity/use limits: no digging, no groundwater use, no well installation without approval
- Monitoring well protection
- Required signage (e.g., call-before-you-dig)
- Annual compliance reporting
- Notice before and after conveyance
- Recordation requirements and successor obligations
Alabama – Environmental Covenants (UECA)
- Recorded UECA covenant in county probate records
- Restrictions on groundwater use, digging, and land use
- Engineering control maintenance
- ADEM Registry listing
- Notice requirements for transfer
Florida – Restrictive Covenants + IC Registry
- Recorded Restrictive Covenant with deed
- Groundwater use prohibitions
- Maintenance of pavement, caps, or containment systems
- Surveyed exhibits with restricted areas
- Inclusion in FDEP’s IC Registry
Georgia – Environmental Covenants (UECA)
- Perpetual environmental covenant
- Industrial-use restrictions
- No-dig zones and groundwater limits
- Required maintenance of engineering controls
- Optional physical markers or signage
Louisiana – RECAP-Driven Controls
- Deed restrictions, servitudes, or recorded notices
- Industrial-only use limitations
- Groundwater use prohibitions
- Engineering control O&M requirements
- Often paired with administrative orders
What This Means for Terminals
Across states, the pattern is consistent:
- ICs must be recorded or officially recognized to be enforceable.
- Operational documents must match the covenant/IC language (SPCC, SWPPP, FRP, MOC, work permits).
- Maps, SOPs, and job aids must display the limits clearly so operations can execute them.
Engineering Controls (In Daily Use)
- Maintenance of impervious surfaces: coatings, liners, sealed joints
- Drain isolation and dewatering SOPs with visual checks and photo logs
- Utility bedding isolation to prevent preferential flow
- Ventilation/housekeeping controls with odor/TVOC triggers
Administrative Controls (Living in the Work System)
- No-dig zones + permit-to-work tied to CMMS or permitting apps
- Groundwater use restrictions via covenant, deed restriction, or policy
- MOC triggers for any paving, drainage, rack, or utility changes
- Compliance calendar for quarterly IC inspections and annual receptor review
When controls are visible and frictionless, they get used. When they’re buried in PDFs, they don’t.
Monitoring Built for Real Operations
- Monitoring network: source wells, interior trend wells, downgradient sentinels
- Frequency: quarterly for Years 1–2, then semiannual/annual
- Parameters: BTEX; periodic geochemistry; vapor indicators if needed
- Stormwater: targeted early-season first-flush checks
- Data: one workbook; locked formulas; consistent charts
The philosophy: fewer bottles, clearer decisions.
Exit Strategy: How You Know You’re Done
Define closure criteria on Day One and coordinated with environmental agency:
- Stable plume from monitoring data
- Geochemistry confirming biodegradation
- Receptors controlled—no exposure pathways
- ICs embedded in SPCC, SWPPP, MOC, and work systems
- A closure report documenting conditions and return-to-action triggers
With clarity upfront, the path to regulatory concurrence becomes smoother and shorter.
Every terminal has legacy challenges—what separates long-running files from successful closures is alignment. When biology, hydrogeology, operations, and institutional controls point in the same direction, risk drops, exposure pathways stay closed, and the remedy becomes self-sustaining.
At PPM Consultants, we’ve helped bulk terminals across the Southeast build MNA programs that work with operations, not against them, and we’ve drafted and implemented ICs in all five states discussed here. If you want to simplify the complex, accelerate closure, or evaluate whether MNA + ICs fits your terminal, contact me at trey.hess@ppmco.com.
We’re here to help you turn “monitoring forever” into measurable progress and clean closure.